On the day of the test, after you have completed the test and have viewed your unofficial Verbal Reasoning and Quantitative Reasoning scores, you will be asked to specify the names of 4 universities or colleges to which ETS will send your GRE General Test scores free of charge. This will be at the test center itself.
If the institution that you want to send your free GRE score to is not listed, you can ask the test center administrator for a form in which you can specify unlisted institutions. If you want the score to be sent to those institutions free, you will have to fill and hand in the form before you leave the test center. It will not be accepted after you leave the test center.